mtd: Blackfin NFC: fix handling of page sizes

Rather than forcing the platform resources to declare the desired page
size, simply use the existing information passed down to us by the higher
layers.  This way we work out of the box with all flash chips that the
kernel knows about.

Signed-off-by: Barry Song <barry.song@analog.com>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>